Internal permanent magnet electrical



g- 1950 M. E. FOGLE 2,518,609

INTERNAL PERMANENT MAGNET ELECTRICAL INSTRUMENT HANISM Filed Dec. 1946 '2 23 munmmumhh I W IIIW'" f This inventionrelates of the permanent magnet, movable coil type" and "more particularly J to" a :novel construction' and assembly of "a -structure that includes the .magnetic 'circuitfand "the bridge membtn' ifor pivotal supportof the movablecoili f QTHB'I prior art includes numerous constructions offelectr'ical;mechanisms of" the type contem- "platedbythis invention but these are open to the general objection that they 'coinpris'e 'a'large Patented Aug. 1 5, 1950 2,51s,sc9;. INTERNALZPERMANENT AGNET ntlzotrnr- 0A1. msrrauwmm MECHANISM.

Marlin-mingle, ma ma, V'J. Aepneatienn em ir 19, 1946; Serial N01. 717,107

number "of"component parts and are costly to assemble. a r

In mechanisms of this class, wherein rotation 0f the =rnovablecoil-is produced by-a minute electric current flowing through-thewinding; it"is essentiakthe' airigapbe free bf any particles or foreign .matter that is likely to interfere with the motion of the coil. Magnetic particles.are. part'i'cularlyiobjectionable' as they adhere tothe-permanent magnet or to the soft 'iron that. forms part'of the magnetic flux path-Iv In presenti'de- .vices .of'this type great care.must be exercised to remove metal burrs that are the result or machining operationssuch as milling, drilling, tapping-etc. Also, the completed device-must zbe inspected-carefully for particles. which may have been'formed and/or dislodged during the assembly operation as is always possible when the parts are assembled b means of screws.

It is also essential that the part forming the mechanism be secured together firmly and permanently as relative displacement of the parts will result in a change of the calibration constants of the mechanism, if not inoperativeness.

A mechanism made in accordance with my invention is not open to the above objections as it comprises a minimum number of parts that are assembled together without screws, bolts, brackets, or etc., and affords an economy of assembly unapproached by existing constructions.

An object of this invention is the provision of an electrical instrument mechanism which can be produced in a small size and at a minimum cost. An object of this invention is the provision of a novel instrument mechanism comprising a permanent magnet, a soft-iron yoke and a bridge member for pivotall supporting a movable coil, said bridge member being disposed between the magnet and the yoke. An object of this invention is the provision of a structure for electrical instruments comprising a permanent magnet and a soft-iron yoke disposed on opposite Sides of a bracket member said parts secured together solely by cement. More specifically it is an object of this inventionto provide an instrument mecha- 3Claims. (cr mp- 9 5 to electrical mechanisms 'nism comprising 'aicylindrical'; permanent magnet; a soft=ir0n yoke "of-substantially "U -shape havingflits ends spaced from the magnet toform magnetic 'flux-gapsya bridge-member positioned 'between'the magnet and the yoke and having offset end extensions overlying the: ends of. the magnet,'and a wire wound, 'movable coil'pivoted between the'offset'end extensions' of the'bridge member for rotation inthe flux gaps.

These and other objects "and "advantages will "be apparent from the following description-when 120? Referring nowto Figures 1, and army novel instrument structure comprises the permanent magnet taken'with the accompanying drawingsfin which:

Figure 1 is an"explod"eol views'howingtlie main partsof adevice made in accordance 'with'my invention;

Figure' Z is an isometric view'o'f the assembled structure*,"and- Figure 3 illustrates the. complete instrument mechanism'onanenlarged scale;

lflthat is'magneti'zedacross' the diameter, aso'ftiron yokejll'fof substantially,,U-shape,,and,a

" ria1. prefera ly brass.

bracketine'inber- [2 made of non ma'gnetic mate- These parts are secured together, as shown in Figure '2," by applying a thin coating of a suitable cement to the contacting surfaces and placing the assembly in a fixture while the cement is polymerized under the action of heat. To afford a greater surface area of contact between the cylindrical magnet 10 and the bracket member [2, the base of the latter is provided with a concave arcuate surface section l3 defined by the ridges l4 and which is formed during the stamping operation by impressing a pair of parallel, longitudinally-extending indentations in the outer face of the bracket base. It is pointed out that the ridges M also serve to position the magnet centrall with respect to the bridge member thereby facilitating the mass production of structures falling Within established limits of tolerance. The curvature of the concave, arcuate surface section in the base of the bracket is made to conform to the circumferential surface of the cylindrical magnet it. There is thus provided contiguous surfaces of relatively large area resulting in a strong, cemented joint between these members. The concave section is and the ridges l4 are so formed that the back surface of the bracket l2 remains substantiall fiat to afiord a stable and large surface area of contact against the inside surface of the yoke ll. By designing the parts as shown I am able to pro- Vide a sturdy, permanent structure which consists of only 3 parts held together solely by cement,

thereby obviating the need for screws, bolts, brackets, etc., and reducing to a minimum the possibility of metal particles becoming lodged in the working area of the mechanism. Although my structure comprises only three parts it provides a complete magnetic circuit and a bridge for pivotal support of a movable element.

The movable element of my instrument mechanism comprises-the wire wound coil l carrying the pointer l6 and pivots H which operate in bearings I8 to afford rotational motion of the coil, as is well known in the art.

Current is brought to the movable coil through the hair.

springs abutments 20, the latter also serving as terminals to which the lead wire 2| may be2-soldered, substantially as shown. The bearings l8 and the IQ having their ends soldered to the a U-shaped yoke of soft-iron secured to the outer face of the bracket base such that the legs of the yoke lie spaced from the magnet to form magnetic flux gaps, the legs of said yoke being spaced apart a distance substantially equal to the width of the bracket base.

2. The invention as recited in claim 1 wherein the soft-iron yoke and the magnet are secured to the bracket base solely by'cement. 10

'3. A111 electrical instrument comprising a U- shaped bracket stamped from a unitary strip of non-magnetic material to provide a base and parallel-extending legs; a pair of parallel, longitudinally-extending indentations pressed into the outerface of the bracket base to thereby 1 formfla concave, arcuate surface section on the abutments are retained in fixed'position by a suitable nut 22. To facilitate the assembly of the movable element the pointer [6 preferably projects through a transverse slot 23 in the bracket member I2. This design also reduces the space requirement when the mechanism is housed in a casing. It is apparent the two ends of the coil [5 must be electrically insulated from each other and this is readily accomplished by floating one of the abutments 20 between suitable insulating washers in the conventional manner.

Having now described my invention certain modifications in the arrangement and location of the parts will be apparent to those skilled in the art without departing from the scope and spirit of the invention as recited in the claims.

I claim:

1. In an assembly for an electrical instrument:

of the permanent magnet-movable coil type the combination of a U-shaped bracket stamped'from a unitary strip of non-magnetic material to provide a base and parallel-extending legs; a pair of parallel, longitudinally-extending indentations pressed into the outer face of the bracket base to thereby form a concave, arcuate surface section on the inner face of the bracket base; a cylindrical magnet having a circumferential surface conforming to and'secured to the said 0011-5,

cave, arcuate surface section of the bracket; and

inner face of the bracket base; a transverse slot inthe bracket base; a cylindrical magnet having a circumferential surface conforming to and REFERENCES CITED The following references are of record in file of this patent:

UNITED STATES PATENTS the Number Name Date 735,168 Stevens Aug. 4, 1903 817,857 Lea Apr. 17, 1906 1,000,942 Pratt Aug. 15, 1911 1,008,549 'Klinckert Nov. 11, 1911 1,920,764 Nickle Aug. 1, 1933 FOREIGN PATENTS Number 7 Country Date 117,154 Austria 'July 8, 1943 

